The invention is in the field of structures for covering large areas, such as full size stadiums, and is particularly directed to a structure having a retractable roof. A structure having a partially retractable roof is illustrated at FIG. 6 of U.S. Pat. No. 4,581,860, in which the applicant herein is the inventor and which is hereby incorporated by reference. Other large-span structures for enclosing stadium-size spaces are discussed in a presentation of the inventor herein to the International Symposium on Spatial Roof Structures at Dortmund, Germany, Sept. 10, 1984 entitled "A Decade of Fabric Tension Structures for Permanent Buildings," and in the 12 references cited at pages 19 and 20 of the presentation. The presentation and its 12 references are hereby incorporated by reference in this specification.
It is believed that there is an increasing demand for covered full-size stadiums and similar structures to make sports and other events independent of the weather. On the other hand, there is a desire to retain the outdoor character of certain events whenever possible, which leads to the demand for retractable roofs. A major difficulty in designing and building a stadium-size structure with a retractable roof is the combination of size and movable parts. Full-size stadiums require free-span roof areas in the area of several hundred thousand feet, and roofs of this size and span to be economically and practically built and used require special structural techniques. In particular, structures of this type can make use of efficient geometries such as domes, saddles, etc., which have a circular, elliptic, or super elliptic boundary condition. Making the roof, or at least the central part of the roof, retractable generally makes those closed structural shapes difficult to implement, although one implementation of a partially retractable roof is shown in said prior patent of the inventor herein. A further consequence of a retractable design is that the movable sections of the roof have to fit the geometry of the structure in the open and closed positions, and this requirement can tend to dominate the geometry choices. One such requirement can be that the edges of the movable roof panels run on straight lines or circles. A further such requirement can be that the superimposed loads, such as wind and snow, have to be safely supported in the open and closed positions, and preferably in any intermediate state as well. Also, rain water has to run off in any position. The combined difficulty of these and other considerations is underscored by the fact that to the knowledge of the inventor herein no retractable stadium roofs have been built so far.
This invention provides a functional, structurally efficient, and economical solution for a full-size stadium roof which, in one nonlimiting example, has a retractable central portion which can open up approximately one-half of the total roof area. This is achieved by the choice of a unique geometric configuration and a unique combination of structural systems, materials and construction methods.
In one exemplary embodiment a central rectangular opening of the roof is covered by two retractable roof panels which are rectangular in plan and can cover an area substantially larger than a football field. The panels are substantially rigid, using trussed steel construction or similar rigid lightweight framing. They are covered with a structural fabric membrane or other lightweight roofing system, and move in the direction of the main axis of the stadium (in the case of a football or soccer field, the main axis is along the long direction of the field, and in the case of baseball it is a line through home plate and third base). The roof panels are high in the middle and low at the ends, thus allowing water to run off in any position of the panels. In the direction of the main axis the retractable panels follow a slight circular curve, to thereby ride on similarly curved tracks supported on track girders. Rollers between the panels and the track girders are arranged to resist downloads, uploads (e.g. from wind uplift), and lateral loads. The movement of the panels is generated by a hoist system similar to that of an elevator or cable car, with cables running along the track girders, which form the inboard edges of two fixed portions of the roof that flank the sides of the stadium field. Two other fixed portions of the roof flank the ends of the stadium field, and are under the curve along which the retractable panels move to their open positions. The track girders are the main longitudinal support members of the roof, running the total length of the stadium. They are suspended from the arches by respective cable systems similar to those used in a stay cable bridge. The upper support points of these suspension cables are a part of an arch which gathers the loads from all of the cables on one side, spanning over the length of the structure. Each arch in turn is laterally supported by a triangulated set of inclined struts which rest on a horizontal edge ring at the stadium perimeter. Horizontal tie cables extend between the two track beams to provide continuity of the system, spanning across the opening in the retractable portion of the roof.
An exemplary embodiment of the invention comprises two tracks which in plan view are parallel to each other and to a first axis of the stadium field, and in elevational view along the first axis are convex and conform an arc of a circle. Two arches in plan view are convex and circumscribe the tracks such that each track is along a chord of a respective arch. In elevational view along the first axis the arches are convex and have curvatures greater than those of the tracks to thereby extend above them. A substantially rigid, laterally extending edge ring in plan view generally follow the outline of the arches and in elevational views along the first axis extends along chords of the arches and tracks. A support, such as a system of columns, can be used to raise the edge ring above grade. The ends of the arches rest on rigid abutments which carry the arch forces into the foundations. Between these abutments the arches are laterally braced by two respective sets of triangulated, inwardly inclined struts, such as steel struts, which rest on the edge ring. The track girders are suspended from the arches by two respective triangulated sets of cables. Horizontal tie cables span from one track girder to another, and two respective sets of stabilizing cables connect the track girders to the edge ring. This system is prestressed and, together with the track girders, forms a sufficiently rigid support for the tracks. The roof panels form substantially rigid space frames covered with fabric or other lightweight roofing material shaped to drain water laterally onto the rigid, fixed portions of the roof at the sides of the stadium field. A system of hoist cables and winches is provided to selectively move the roof panels toward and away from each other along the tracks, to thereby close or open the roof of the structure.